The power amplifier is typically the last stage in the processing of signals for transmission from a wireless base station. Power efficiency is a critical performance metric for these and similar amplifiers. In a base station, for example, the power amplifiers may account for as much as half the total power expenditure. Both to reduce operating costs and to mitigate thermal loads, there is a need to improve the efficiency of power amplifiers.
Several well-known techniques have been applied to improve power efficiency, including the use of Doherty amplifier designs, envelope elimination and restoration, and linear amplification with nonlinear components. Another possible approach is to use Class S switching amplifiers for power amplification. Such amplifiers are attractive because they interface readily with the digital processing that is becoming ubiquitous in wireless base stations, and because Class S amplifiers have theoretical efficiencies near 100%.
One factor that may limit the suitability of Class S amplifers is the coding efficiency. The coding efficiency determines how much of the total power expenditure in the amplifier is converted to electromagnetic energy within the desired spectral band, and not instead dissipated in out-of-band radio emission and through static and dynamic switching losses. Various approaches to coding have proven useful, such as sigma-delta modulation and pulsewidth modulation. However, there remains a need for further approaches to coding that offer the possibility of high efficiency.